The invention relates to a false-twisting nozzle for pneumatic false-twist spinning having a nozzle body formed of one or several segments which is provided with a yarn duct extending through it, at least one blow duct leading tangentially into the yarn duct.
In the case of false-twisting nozzles, it is to be endeavored that the blow ducts lead into the yarn duct in a tangential manner that is as precise as possible and extend as little as possible toward the center of the yarn duct. As a result, it is to be achieved that a clearly defined air whirl develops which grips the yarn roving formed of a drafted sliver at its outer circumference and sets it into rotations. If the blow jets deviate from the tangential direction and/or exit at a relative large distance from the interior wall of the yarn duct, there is the risk that, as a result, the order of the fibers in the fiber roving will be impaired. It is therefore endeavored to provide a blow-in cross-section that is as small as possible and a blow-in direction which is as precisely tangential as possible. However, up to now, it has been difficult to meet both requirements simultaneously.
It is known from German Patent Document DE-C 37 34 566 to provide blow ducts as bores which are to have a diameter of from 0.2 mm to 0.6 mm. Particularly, if the diameters are to amount to less than 0.4 mm, there is the risk that the bore extends in such a way that the tangential direction cannot be maintained sufficiently reliably.
It is also known from German Patent Documents DE-A 37 32 708, DE-A 37 18 656 to provide the blow ducts between two segments of a nozzle body, in which case slots are worked into one of the segments which are covered by the other segment. In this type of construction, it is also difficult to ensure a precise aligning of the slots if the slot widths are small.
It is an object of the invention to provide a false-twisting nozzle of the initially mentioned type which has one or several blow ducts with a precisely tangential alignment with respect to the yarn duct and with a small dimension from the interior wall of the yarn duct toward the center of the duct.
This object is achieved according to preferred embodiments of the invention in that, for the reduction of the cross-section of the outlet opening at least one part of the interior wall of the blow duct is provided with a coating.
As a result, it is possible to produce the blow duct, by means of cutting, first with a relatively large dimension so that the directional precision can be ensured. Subsequently, the final cross-section will then be determined by means of the coating applied to the interior wall or a part of the interior wall so that, despite the originally larger cross-section, a very small cross-section may be obtained without the result of a loss of directional precision.
In a further development of the invention, it is provided that nickel is used as the coating which is chemically deposited on the interior wall of the blow duct. A nickel layer of this type can be applied with very high precision even in the case of complicated shapes so that the original precision will not be lost.
In a further development of the invention, it is provided that the at least one slot leads into a section of the yarn duct which is also provided with the coating. On the one hand, this results in the advantage that the shape of the mouth areas toward the interior wall of the yarn duct is maintained in the produced shape, while, in addition, the advantage is achieved that a protection against wear can be obtained in this area as a result of the coating, particularly if diamond grains are embedded in the nickel coating.
In a further development of the invention, it is provided that the blow duct or blow ducts are machined in between two abutting segments of the nozzle body and that, for developing a blow duct, one of the segments is provided with a slot which is open in the direction of the other segment, in which case only the slot area is provided with a coating. This type of a slot can be made with high directional precision up to a slot width of 0.4 mm by means of a commercially available front-milling tool. By means of the coating, the desired smaller slot widths are then created. In a further development, it is provided that the slot has a U-shaped cross-section, and that the depth of the slot is larger than its width. As a result, it is possible to produce the blow duct with a sufficiently large cross-section for the blowing-out of a sufficient air volume while, on the other hand, the dimension of the blow duct in the direction toward the center of the yarn duct can be kept small.